A person who makes a decision should be unbiased and act in good faith. He therefore can not be one of the parties in the case, or have an interest in the outcome. This is expressed in the Latin maxim, nemo iudex in causa sua: "no man is permitted to be judge in his own cause"

This a fundamental principle of private law in the UK, and also I believe in Canada … I don't know about the USA.

Accordingly one would expect that if a mentor is insulted, s/he would report it in the usual way, and another mentor would deal with it.